The present invention relates to an optical disc unit for recording and reproducing data on and from an optical disc that has a plurality of recording layers.
A digital versatile disc (referred to as DVD hereinafter) that is currently standardized has two layers on one surface thereof. When the two layers are formed on one surface, recording layers are previously laminated on each of two discs having a thickness of 0.6 mm. A disc with an aluminum film having a high reflection rate and a disc with a translucent metal reflection film are bonded together. Thus, it is possible to access the plurality of recording layers from one surface.
Access to each recording layer can be made and thereby information recorded thereon can be read by moving an objective lens relative to the two-layer disc to bring the objective lens into focus to a focused point (hereinafter referred to focused focal point) at a position of an objective lens for each recording layer based on a focus error signal. This interlayer movement of a focused focal point (hereinafter referred to interlayer jump) is disclosed in, for example, JP-A-H09-50630 and JP-A-11-345420.